1. Field of the Invention
The present invention relates to a method of manufacturing optical sensors.
2. Description of the Related Art
Optical sensors manufactured by a wafer level chip size package (WLCSP) process are known. An optical sensor manufactured by the WLCSP process is obtained by fixing a wafer-state semiconductor substrate including image pickup devices and a light transmissive substrate together and dividing the fixed substrates into individual chips. Japanese Patent Laid-Open No. 2006-147864 discloses a structure and method of manufacturing wafer level chip size packages (WLCSPs) that contribute to a reduction in size of optical sensors.
Japanese Patent Laid-Open No. 2010-056319 discloses a method in which a groove of about 150 μm is formed in a resin layer between dicing portions and image pickup devices to reduce warping of WLCSPs, in the wafer level, due to the difference in coefficient of linear expansion and reduce warping after the wafer is divided into pieces.
In the above-described method of manufacturing optical sensors, a semiconductor wafer and a light-transmissive substrate are fixed to each other with a fixing member. However, it has been difficult to suppress bubbles generated between the fixing member and the light-transmissive substrate after the wafer and the substrate are fixed. The bubbles decrease the bonding strength of bonding surfaces when heated in the subsequent step and decrease the yield because of separation of the semiconductor wafer and the light-transmissive member. Furthermore, even after the integrated wafer and substrate are divided into pieces, because the bubbles remaining between the adhesive layer and the glass substrate degrade the air-tightness of the semiconductor devices, the reliability of the semiconductor devices is decreased.